PROCFS(5) BSD File Formats Manual PROCFS(5)NAMEprocfs — process file system
proc /proc procfs rw 0 0
The process file system, or procfs, implements a view of the system
process table inside the file system. It is normally mounted on /proc,
and is required for the complete operation of programs such as ps(1) and
The procfs provides a two-level view of process space, unlike the previ‐
ous FreeBSD 1.1 procfs implementation. At the highest level, processes
themselves are named, according to their process ids in decimal, with no
leading zeros. There is also a special node called curproc which always
refers to the process making the lookup request.
Each node is a directory which contains the following entries:
Each directory contains several files:
ctl a write-only file which supports a variety of control operations.
Control commands are written as strings to the ctl file. The
control commands are:
attach stops the target process and arranges for the sending
process to become the debug control process.
detach continue execution of the target process and remove it
from control by the debug process (which need not be the
run continue running the target process until a signal is
delivered, a breakpoint is hit, or the target process
step single step the target process, with no signal delivery.
wait wait for the target process to come to a steady state
ready for debugging. The target process must be in this
state before any of the other commands are allowed.
The string can also be the name of a signal, lower case and with‐
out the SIG prefix, in which case that signal is delivered to the
process (see sigaction(2)).
The procctl(8) utility can be used to clear tracepoints in a
dbregs The debug registers as defined by struct dbregs in
<machine/reg.h>. dbregs is currently only implemented on the
etype The type of the executable referenced by the file entry.
file A symbolic link to the file from which the process text was read.
This can be used to gain access to the process' symbol table, or
to start another copy of the process. If the file cannot be
found, the link target is ‘unknown’.
fpregs The floating point registers as defined by struct fpregs in
<machine/reg.h>. fpregs is only implemented on machines which
have distinct general purpose and floating point register sets.
map A map of the process' virtual memory.
mem The complete virtual memory image of the process. Only those
address which exist in the process can be accessed. Reads and
writes to this file modify the process. Writes to the text seg‐
ment remain private to the process.
note Used for sending signals to the process. Not implemented.
notepg Used for sending signal to the process group. Not implemented.
osrel Allows read and write of the kernel osrel value assigned to the
process. It affects the compatibility shims that are turned on
and off depending on the value. Initial process value is read
from the ABI note tag in the executed ELF image, and is zero if
the tag not supported by binary format or was not found.
regs Allows read and write access to the process' register set. This
file contains a binary data structure struct regs defined in
<machine/reg.h>. regs can only be written when the process is
rlimit This is a read-only file containing the process current and maxi‐
mum limits. Each line is of the format rlimit current max, with
-1 indicating infinity.
status The process status. This file is read-only and returns a single
line containing multiple space-separated fields as follows:
· command name
· process id
· parent process id
· process group id
· session id
· major,minor of the controlling terminal, or -1,-1 if there is
no controlling terminal.
· a list of process flags: ctty if there is a controlling ter‐
minal, sldr if the process is a session leader, noflags if
neither of the other two flags are set.
· the process start time in seconds and microseconds, comma
· the user time in seconds and microseconds, comma separated.
· the system time in seconds and microseconds, comma separated.
· the wait channel message
· the process credentials consisting of the effective user id
and the list of groups (whose first member is the effective
group id) all comma separated.
· the hostname of the jail in which the process runs, or ‘-’ to
indicate that the process is not running within a jail.
In a normal debugging environment, where the target is fork/exec'd by the
debugger, the debugger should fork and the child should stop itself (with
a self-inflicted SIGSTOP for example). The parent should issue a wait
and then an attach command via the appropriate ctl file. The child
process will receive a SIGTRAP immediately after the call to exec (see
Each node is owned by the process's user, and belongs to that user's pri‐
mary group, except for the mem node, which belongs to the kmem group.
/proc normal mount point for the procfs.
/proc/pid directory containing process information for
/proc/curproc directory containing process information for the
/proc/curproc/cmdline the process executable name
/proc/curproc/ctl used to send control messages to the process
/proc/curproc/etype executable type
/proc/curproc/file executable image
/proc/curproc/fpregs the process floating point register set
/proc/curproc/map virtual memory map of the process
/proc/curproc/mem the complete virtual address space of the process
/proc/curproc/note used for signaling the process
/proc/curproc/notepg used for signaling the process group
/proc/curproc/osrel the process osrel value
/proc/curproc/regs the process register set
/proc/curproc/rlimit the process current and maximum rlimit
/proc/curproc/status the process' current status
To mount a procfs file system on /proc:
mount -tprocfs proc /proc
SEE ALSOprocstat(1), mount(2), sigaction(2), unmount(2), procctl(8), pseudofs(9)AUTHORS
This manual page written by Garrett Wollman, based on the description
provided by Jan-Simon Pendry, and revamped later by Mike Pritchard.
BSD September 22, 2009 BSD